1. Field of the Invention
The present invention relates to a tension spring clamp having a housing in which a tension spring is attached by its bearing arm to a power terminal that protrudes through a clamping window in a frontal section of a spring arm of the tension spring. More particularly, the present invention relates to the housing being furnished with a conductor insertion aperture below the power terminal that in a clamped position faces an open area of the clamping window in the spring arm, above the power terminal, and level with a top centered range of the spring arm that is biased towards the bearing arm, an actuating aperture for inserting a tool for biasing the spring arm down onto the bearing arm, and a test tap aperture between the conductor insertion aperture and the actuating aperture through which a contact pin of a test plug may be inserted to contact the power terminal.
2. Description of the Prior Art
In known tension spring clamps the test tap aperture of the housing is located level with a frontal extremity of the power terminal that protrudes through the clamping window in the spring arm, wherein an extremity of the contact pin of the test plug is placed on only one point of the power terminal. Such an arrangement is known as a xe2x80x9ctouch control contactxe2x80x9d, which only ensures a reliable contact if the extremity of the contact pin of the test plug is forced by pressure against the frontal extremity of the power terminal. For this reason, the test plug must be held manually throughout a test tapping operation. If the test plug is released, transition resistances at the contact point may rise, which in turn lead to incorrect measurements.
The object of the present invention is therefore to provide a tension spring clamp with which a reliable contact of the test plug""s contact pin with the power terminal is assured even if the test plug is released.
This object is solved in a tension spring clamp according to the present invention wherein the test tap aperture for insertion of the test plug""s contact pin is conformed as a hollow cylinder, wherein an extension of a cylinder axis thereof runs along an inner side of the bearing arm of the tension spring that is facing away from the power terminal, and further in that besides the clamping window, an insertion window for the test plug""s contact pin is provided in the frontal section of the spring arm of the tension spring, and still further in that the power terminal is provided with a deformation that protrudes into an insertion channel in such a manner that the contact pin that is inserted and retained in the test tap aperture is constrained adjacent thereto along its entire length.
It is important for the purposes of the present invention that when the contact pin of the test plug is inserted, and passes along the deformation of the power terminal, the contact pin is subjected to a small elastic radial excursion, so that the contact pin is brought into sprung contact with the deformation of the power terminal, which ensures reliable contact between the contact pin and the power terminal even if the test plug is released. In the contact position, the test plug""s contact pin projects inside the tension spring of the tension spring clamp, and to accommodate such an additional insertion aperture must be provided in the frontal section of the spring arm of the tension spring. At the same time, however, the test tap is obstructed neither by the electrical conductor located in the conductor insertion area of the tension spring clamp nor by any tool that may be inserted into the actuating aperture of the clamp housing. Finally, the very fact that contact between the power terminal and the contact pin takes place inside the tension spring assures a particularly reliable test tap without a need to hold the test plug by hand throughout the operation.
In order to ensure that the contact tip of the test plug may be reliably inserted as far as the deformation of the power terminal regardless of a respective excursion of the spring arm, the insertion aperture in the frontal section of the spring arm of the tension spring must allow adequate play. To this end, therefore, the insertion aperture advantageously has a form of an elongated hole stretching in a direction of sprung displacement of the frontal section of the spring arm, and the elongated hole ultimately-opens into the clamping window of the spring arm.
It must further be assured that the tension spring clamp is seated securely on the power terminal. To this end, the bearing arm of the tension spring is advantageously furnished with a through-hole, through which the deformation of the power terminal protrudes, and which is form-fit to a shape of the through-hole. In this way, the deformation of the power terminal serves a dual purpose, not only assuring contact of the test plug""s contact pin, but also acting as a mechanical restraint for the tension spring. In an advantageous configuration of the present invention, the deformation in the power terminal consists of a knuckle impressed therein, which is upset so that an area of its free extremity inside the bearing arm clasps an edge of the through-hole. Moreover, a process of upsetting the free frontal face of the knuckle-shaped deformation of the power terminal may be advantageously used to impress a groove-shaped profile therein, particularly a V-groove, in an area of which the test plug""s contact pin makes contact as the length of the contact pin is adjacent to the sides of this profile.
In the following, the invention will be explained in greater detail with reference to the drawing and an exemplary embodiment thereof.